enabled message storing into error message list
for 'drop table' command


mysql-test/r/warnings.result:
  test result
mysql-test/t/warnings.test:
  test case
sql/sql_table.cc:
  We should skip error sending then we should return
  warnings to client as some functions may send its
  own errors, so we should set no_warnings_for_error= 0
  only in case of warning.
  The fix is to enable message storing into error message
  list for 'drop table' command(only for error case).
tests/mysql_client_test.c:
  test fix